The big mistake we made in Iraq and Afghanistan (other than going in) was not partitioning them.
Partitioning solved the Yugoslavia problem. Or going back the Austro Hungary problem.
Iraq should have been divided into three countries. Shia, Sunni and Kurd. As it is the Kurds have formed their own country anyhow. But the Sunnis and Shias will keep killing each other for all eternity. There is a proxy war between KSA (Sunni) and the mad mullahs (Shia) that is being fought out everywhere that there is Islam.
In Afghanistan we had this silly idea of forcing democracy on them. Something they don't need or want. This has cost us hundreds of billions of dollars and thousands of lives. We should have split the place up as a federation under the various warlords and supported those who played ball and punished those who didn't. This would have been far faster, far cheaper and would have brought civilisation to the place far sooner.
The only workable solution to Syria is partition. They hate each other far too much to work together any time soon. On the ground they are already partitioned. Kurds in the north. Alawites in Damascus and Homs and along the coast. Sunnis along the Euphrates and in Allepo and the surrounding area.
A big problem is that when the colonialists drew their lines on the map they split up the Kurdish people. Destiny is that they will be reunited and now would be a good time. They are already self governing in Iraq and Syria. What is needed is for Turkey to give up their Kurdish territory to this new country, which is exactly what the Turks don't want. But the reality is that the Kurds have been fighting for a long time now and will continue to fight till they get their state. The Turks would do vastly better in every way if they accepted this.